1. Field of the Invention
The present invention relates to a composite chassis frame and a method for manufacturing the chassis frame. More particularly, it relates to a composite chassis frame and a method for manufacturing the chassis frame, which prevents thermal deformation of a steel core material and has sufficient rigidity and stiffness.
2. Description of Related Art
In the case of electric vehicles or hybrid vehicles, the vehicles need to be reduced in weight to improve fuel efficiency. However, since components formed of metal occupy about 70% of the whole weight, there is a limitation in modifying design to reduce the weight of a vehicle. Accordingly, many studies are being conducted to replace metal materials with composite materials that are lightweight materials.
However, there are difficulties in manufacturing the frame of a small-to-medium sized bus using composite materials.
Regarding strength, the yield strength of composite materials such as Carbon Fiber Reinforced Plastic is similar to that of a steel frame. However, since the young's modulus (E) of the composite material that is one of material properties in terms of stiffness reaches about 20% to about 30% of that of the steel frame, the thickness or the sectional size of the composite material has to be increased to maintain a stiffness equal to that of the steel frame.
On the other hand, frames of commercialized vehicles equipped with suspensions need to meet the following two requirements.
First, deformation due to the axle load needs to be small. When the stiffness gets greater, the frames are less deformed from given loads, and the handling stability improves because a hard point of the suspension does not move.
Second, a suspension mounting bracket and a frame are mounted with hardware such as bolts. When the thread of bolt is directly created on a composite material frame for fastening, the thread may be abraded, making it to secure a bolt fastening strength. Accordingly, when a commercialized vehicle frame is configured using composite materials, the commercialized vehicle frame can perform its function only when some steel materials are inserted into the frame to increase the efficiency of stiffness and the coupling strength of the bolts.
However, when a composite material is used as an external skin, and steel or foam materials are inserted into the inside to undergo a high temperature formation, deformation of steel may occur, causing a difficulty in adjusting the dimensions of the composite material frame.
Hereinafter, a typical composite material will be described in more detail.
As shown in FIG. 1, frames for low-floor buses are formed of metal to serve as a backbone of a vehicle, and support a suspension such as a leaf spring.
Also, since the frame of the low-floor bus does not have an integral structure in which a front side is connected to a rear side, but have a structure in which a front frame 100 and a rear frame 200 are connected to a center floor 300, a suspension is generally coupled to the front frame and the rear frame by bolting.
Accordingly, the steel frame will be not limited by bolt mounting.
FIG. 2 is a view illustrating a rear frame of a low-floor bus. A rear frame 200 includes a floor connector 202, a suspension connector 201, and an upper body connector.
When the rear frame is formed of composite materials, Carbon Fiber Reinforced Plastic (CFRP) or Glass Fiber Reinforced Plastic (GFRP) used as a skin, and steel and foam as cores are laminated inside the frame mold (not shown), and are hardened at a temperature of about 100° C. to about 150° C. to manufacture a composite materials rear frame.
When the frame of the suspension connector 201 is manufactured, the composite materials skin, and steel and internal core materials are laminated and cured at a high temperature at once. In this case, a stiffness difference of each material may cause deformation of the core materials, reducing the quality of the product.
Accordingly, as shown in FIG. 3, since the steel core material laminated together with the foam cannot become vertical due to deformation of the foam used as the core material, requirements for mounting a suspension cannot be satisfied.
In the case of a typical product in which foam and steel materials are directly bonded and external composite materials are laminated to cure at a high temperature, there is a limitation in that the steel material is deviated from its vertical position together with the deformation of the foam material due to the stiffness difference between the foam material and the steel material.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.